This invention relates to a method for making an article having an irradiated adhesive on a radiation degradable substrate where the substrate has no substantial degradation. More specifically this invention relates to a drum transfer method for adhesive irradiation by electron beam.
Adhesives, including pressure-sensitive adhesives, and heat activatable adhesives are well known in the art for bonding to a variety of materials such as metals, painted surfaces, plastics, and the like. Adhesives are designed to meet various requirements by balancing their viscous and elastic properties to result in a balance of shear, peel, and tack properties. Pressure-sensitive adhesives generally adhere with light pressure and are tacky at the use temperature. Heat activatable adhesives may adhere with light pressure and be slightly tacky at the use temperature, or may require elevated temperatures or pressures to adhere to another material.
Crosslinking occurs when a polymer, that may be of a low molecular weight, is subjected to ionizing radiation that links the polymer chains together and increases the effective molecular weight. Adhesives can be crosslinked to obtain the desired balance of properties.
Briefly, the present invention provides a method for making a substrate coated with an adhesive, comprising: applying an electron beam modifiable adhesive layer onto a repeatably reusable transfer surface; irradiating the adhesive layer with an electron beam to chemically modify the adhesive layer; and transferring the irradiated adhesive layer to a substrate. In one embodiment, the adhesive is applied to a release surface before applying the adhesive to the repeatably reusable transfer surface.
In another aspect, the present invention provides an adhesive coated web, comprising: a substrate having at least one component susceptible to electron beam radiation degradation selected from the group consisting of cellulose-based non-woven fabrics, cellulose-based woven fabrics, paper, polyisobutylene films, polypropylene films, polypropylene-based nonwovens, polytetrafluoroethylene films, vinyl films, and combinations thereof, having no electron beam radiation modification; and an adhesive layer attached to the substrate and in contact with a radiation degradable component of the substrate, the adhesive having an electron beam modified composition and containing no substantial quantity of chemical, thermal, or ultraviolet crosslinking agent. The adhesive is selected from the group consisting of acrylics, natural rubbers, polybutadienes, polyisoprenes, styrene/butadiene copolymers, styrene/isoprene copolymers, and silicones.
This invention also provides a new adhesive coated web having a substrate having at least one component susceptible to electron beam radiation degradation having no electron beam radiation modification, and an adhesive layer having an electron beam modified composition wherein the electron beam modified adhesive layer has an electron beam modification profile selected from the group consisting of an increasing degree of crosslinking through the adhesive thickness from a surface toward the substrate, a substantially uniform degree of crosslinking through the adhesive thickness, a decreasing degree of crosslinking through the adhesive thickness, and a peak level of crosslinking within the adhesive between the surface and the substrate; and wherein the resulting construction flexibility is not substantially different from the construction flexibility of a similar adhesive coated web having had no electron beam modification. In essence, any possible electron beam modification profile can be achieved with the present invention without degrading the substrate.
Another embodiment of the present invention includes a new adhesive coated web having an electron beam modified adhesive layer and a substrate that has a different release characteristic on each major surface.
As used herein:
xe2x80x9cradiation degradablexe2x80x9d describes a material the durability or flexibility of which decreases due to exposure to electron beam radiation at a dose and accelerating potential needed to achieve a desired modification of an electron beam modifiable adhesive layer;
xe2x80x9celectron beam modifiablexe2x80x9d means susceptible to chemical changes resulting from electron beam irradiation, for example forming free radicals, chemically activating a skin layer, crosslinking, curing, increasing or decreasing the molecular weight of a polymer, polymerizing oligomers or monomers, and the like; thus, an electron beam modification of a material would include changes such as, for example, embrittlement, crazing, cracking, formation of a skin layer, bond sission, and formation of degradation species such as oxides;
xe2x80x9cstructured surfacexe2x80x9d means a surface having a multiplicity of recessed structures, features or convolutions made by any process, including electroforming, embossing, etching, molding, machining, or sandblasting, the average depth of which is between 1 and 2000 micrometers (xcexcm) over the majority of its area, but preferably over 75% or more of its area and more preferably over 90% or more of its area, which may or may not also comprise occasional larger recessed structures.
It is an advantage of the present invention to provide a method of making electron beam modified adhesive layers on radiation vulnerable substrates while not exposing the substrate to electron beam energy. This permits manufacturing constructions having the advantages inherent in the electron beam process, with various electron beam modification profiles, without the adverse effects on the substrate associated with electron beam energy, and without the use of a carrier material.